Smectite to illite conversion by hydrous pyrolysis
Authors: Roaldset, E.; Wei, He; Grimstad, S.
Source: Clay Minerals, Volume 33, Number 1, 1 March 1998 , pp. 147-158(12)
Publisher: Mineralogical Society
Abstract:Experimental illitization of smectite has been simulated by means of hydrous pyrolysis, using a smectite-rich starting material from a Lower Tertiary claystone from the Oseberg field, North Sea. The <2 m fraction was subjected to hydrous pyrolysis using KCl solutions at concentrations of 1.0 and 0.01 N, temperatures from 180-350°C and reaction times from 24-72 h. The conversion of smectite into illite has been identified by XRD analysis of the pyrolysed products. It was clearly demonstrated that the K+ concentration ((K+1)) and temperature are the major factors controlling the rate and extent of illitization. The distributions of activation energies around 33 kcal/ mol and frequency factors in the range of 10+8 to 10+9 s-1 have been calculated by applying a parallel reaction model. However, geological modelling and comparison with buried smectite clays indicates that both 1.0 N and 0.01 N KCl are too high in K+ content compared to the pore-water. The results suggest that dilute KCl solution close to pore-water should be used in hydrous pyrolysis to obtain proper kinetic models.
Document Type: Research Article
Affiliations: Department of Geology and Mineral Resources Engineering, Norwegian University of Science and Technology (NTNU), N-7034 Trondheim, Norway
Publication date: 1998-03-01